In recent years, methods of manufacturing a printed wiring board in which the transmission performance of electric signals in a through hole is improved by splitting a conductive region in the through hole of a multilayered printed wiring board (hereinafter referred to as a printed wiring board provided with split through holes) by arranging a plating resist in a predetermined position in the inner layer through holes have been proposed.
Patent Document 1 discloses the method to prevent forming of a straight conductive material in via structure (corresponding to the “through hole” referred to in the present invention) by providing one or more intended voids made of plating resists in via structure. As a result, the forming of a conductive material in via structure is limited only on a region required for the transmission of electric signals. Application of such a method is advantageous because a desired multilayered printed wiring board can be manufactured by “lamination all at once”. In the conventional manufacturing method of a multilayered printed wiring board, as printed-wiring boards (PCB) are sequentially laminated a plurality of sub-assemble PCBs are individually prepared, followed by laminating sub-assemble PCB to finish a multilayered wiring board. In the manufacturing method, a plurality of laminating steps are necessary until intended multilayered structure is achieved, and after each lamination, additional process for plating through holes and/or via structure may be also required. So, increased manufacturing cost and cycle time have been disadvantage.
FIG. 10 of Patent Document 1 is “a drawing showing stacked PCB in specific embodiment, and a split plated via structure are formed by selectively providing plating resist in gap formed in a conductive layer and an adjacent dielectric layer of a sub-composite structures”. The plated via structure 1030 in FIG. 10 is split into a plurality of electrically isolated portions (1030a and 1030b) by selectively providing plating resist in a sub-composite structure used in manufacturing of the stacked PCB.